Spinal surgery system and method

ABSTRACT

Apparatus and method for minimally invasive spinal surgery employs an elongated flexible guide element inserted so as to pass in through a first lateral posterior incision, through the spinal column anterior to the spinal cord, and out through a second lateral posterior incision contralateral to said first incision. The guide element is used to guide various elements to a desired position within the spinal column as part of the surgical procedure. Preferably, two hollow rigid tubes rigidly coupled outside the body in converging relation are used to define a working gap within the spinal column through which the guide element passes. This provides a platform for manipulation of tissues and introduction of implants anterior to the spinal cord. Procedures described include reinforcement of a degenerative intervertebral disc and restoration of a damaged vertebral body.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to spinal surgery and, in particular, it concerns a system and method for performing various minimally invasive spinal surgical procedures.

The past several years have witnessed a multitude of novel ideas and techniques for improved care for patients with spinal conditions. Some of these advances have improved the quality of life of patients suffering from degenerative disk disease with disabling low back pain. The current trend is towards less invasive approaches with less iatrogenic soft-tissue morbidity, as compared to traditional procedures with or without fusion of vertebral bones.

Despite a wide range of procedures performed today as minimally invasive spinal surgery (“MISS”) procedures, there remain fundamental limitations to the available options in a number of respects. Firstly, while a posterior approach is preferred for minimizing iatrogenic soft-tissue morbidity, it has been found difficult to achieve precise positioning of devices anterior to the spinal cord using a posterior approach. Furthermore, the available techniques for anchoring implants in position within the spinal column are limited in their reliability and tend to generate problematic local debris.

There is therefore a need for an apparatus and method for minimally invasive spinal surgery which would provide a guide element for providing a well defined reference location within the spinal column for performance of a MISS procedure anterior to the spinal cord.

SUMMARY OF THE INVENTION

The present invention is an apparatus and method for minimally invasive spinal surgery, and corresponding surgical techniques which can advantageously be implemented using the apparatus and method of the invention.

According to the teachings of the present invention there is provided, an apparatus for use in performing a minimally invasive spinal surgical procedure via a pair of bilateral stab wounds on either side of a subject region of the spine of a patient, the apparatus comprising: (a) a first hollow rigid tube having a proximal end and a distal end, the distal end for insertion through a first of the stab wounds; (b) a second hollow rigid tube having a proximal end and a distal end, the distal end for insertion through a second stab wound in the back of a patient; (c) a rigid coupling for rigidly coupling the first and second tubes such that the tubes converge towards the distal ends but maintain a predefined gap between the distal ends; and (d) an elongated flexible guide element for deployment so as to extend through the first hollow tube from the proximal end to the distal end, to traverse the gap and to extend through the second hollow tube from the distal end to the proximal end.

According to a further feature of the present invention, the first and second tubes are implemented as substantially straight hollow tubes.

According to a further feature of the present invention, the distal ends of the first and second tubes are implemented as inward-facing beveled ends.

According to a further feature of the present invention, the distal ends of the first and second tubes are curved towards the gap.

According to a further feature of the present invention, there is also provided a removable trocar removably receivable within each of the first and second tubes for facilitating insertion of the first and second tubes in the back of the patient.

According to a further feature of the present invention, the guide element is asymmetric under rotations about its length.

According to a further feature of the present invention, there is also provided a retractable drilling device removably associated with at least one of the first and second tubes and configured for drilling a connecting channel through the gap for insertion of the guide element.

According to a further feature of the present invention, the drilling device is implemented as a directional drilling device configured for drilling in a direction non-parallel with a central bore of the tube.

According to a further feature of the present invention, there is also provided a plurality of beads detachably associated with the guide element, and a release mechanism for releasing the plurality of beads from the guide element in the gap.

According to a further feature of the present invention, the plurality of beads are interconnected as at least one chain of beads such that the plurality of beads remain interconnected after release from the guide element.

According to a further feature of the present invention, the plurality of beads are formed from a material having a porous surface with pores of width 50-100 microns, and more preferably of width 70-80 microns.

According to a further feature of the present invention, there is also provided a net element deployable within the gap around the guide element so as to contain the plurality of beads within a predefined containment volume.

According to a further feature of the present invention, the plurality of beads are each formed with at least one surface configured to promote scar tissue formation, and wherein the net element is formed to allow penetration of cells to facilitate scar tissue formation at the at least one surface.

According to a further feature of the present invention, there is also provided a pair of flexible elongated fixation appendages associated with the net element so as to be locatable within the first and second tubes and adapted for fixation to bone surfaces after removal of the first and second tubes to fix the net element in a required position.

According to a further feature of the present invention, there is also provided a directional tissue compression device removably deployable along at least one of the first and second tubes, the directional tissue compression device including at least one compression element configured for applying pressure to a slice of tissue located adjacent to the gap and extending away from the first and second tubes so as to form a cavity.

According to a further feature of the present invention, there is also provided an expandably fillable element for deployment in the cavity.

According to a further feature of the present invention, the expandably fillable element includes perforations configured for allowing release of a small proportion of a filler material to enhance fixation of the expandably fillable element.

According to a further feature of the present invention, the expandably fillable element includes a pair of flexible elongated fixation appendages locatable within the first and second tubes, the fixation appendages being adapted for fixation to bone surfaces after removal of the first and second tubes to fix the expandably fillable element in a required position.

There is also provided, according to the teachings of the present invention, a method for performing a minimally invasive spinal surgical procedure, the method comprising the steps of: (a) inserting an elongated flexible guide element such that the guide element passes in through a first lateral posterior incision, passes through the spinal column anterior to the spinal cord, and passes out through a second lateral posterior incision contralateral to the first incision; and (b) employing the guide element to guide at least one element to a desired position within the spinal column as part of the surgical procedure.

According to a further feature of the present invention, the method also includes: (a) inserting a first hollow rigid tube through the first incision; (b) inserting a second hollow rigid tube through the second incision; and (c) rigidly coupling the first and second tubes in spatial relation so as to define a gap between distal ends of the tubes, wherein the inserting of the guide element is performed via the first and second tubes.

According to a further feature of the present invention, the first and second tubes are implemented as substantially straight hollow tubes.

According to a further feature of the present invention, the first and second tubes are implemented with beveled ends, the rigidly coupling being performed so that the beveled ends face inwards towards the gap.

According to a further feature of the present invention, the first and second tubes are implemented with curved ends, the rigidly coupling being performed so that the curved ends curve inwards towards the gap.

According to a further feature of the present invention, a removable trocar is inserted into each of the first and second tubes for facilitating the inserting of the first and second tubes, the trocar being removed prior to the inserting of the guide element.

According to a further feature of the present invention, a retractable drilling device inserted via one of the first and second tubes is employed to drill a connecting channel through the gap for insertion of the guide element.

According to a further feature of the present invention, the drilling device is implemented as a directional drilling device configured for drilling in a direction non-parallel with a central bore of the tube.

According to a further feature of the present invention, the guide element is asymmetric under rotations about its length.

According to a further feature of the present invention, the guide element is inserted through an intervertebral disc.

According to a further feature of the present invention, the at least one element includes a plurality of beads detachably associated with the guide element, the plurality of beads being released for delivery to a desired position within the intervertebral disc.

According to a further feature of the present invention, the plurality of beads are interconnected as at least one chain of beads such that the plurality of beads remain interconnected after release from the guide element.

According to a further feature of the present invention, the plurality of beads are formed from a material having a porous surface with pores of width 50-100 microns, and more preferably of width 70-80 microns.

According to a further feature of the present invention, the at least one element includes a net element deployable around the guide element, the net element being deployed within the intervertebral disc so as to contain the plurality of beads within a predefined containment volume.

According to a further feature of the present invention, the plurality of beads are each formed with at least one surface configured to promote scar tissue formation, and wherein the net element is formed to allow penetration of cells to facilitate scar tissue formation at the at least one surface.

According to a further feature of the present invention, the net element is formed with a pair of flexible elongated fixation appendages, the net element being deployed with the fixation appendages extending through within the first and second contralateral incisions, respectively, the method further comprising, after release of the plurality of beads into the net element, attaching the fixation appendages to contralateral regions of bone so as to fix the net element in a required position.

According to a further feature of the present invention, the guide element is inserted through a vertebral body.

According to a further feature of the present invention, the guide element is inserted through a bore drilled in a first pedicle of the vertebra, passes through the vertebral body and passes out through a bore drilled in a second pedicle of the vertebra.

According to a further feature of the present invention, a directional tissue compression device is introduced into the vertebral body and operating the directional tissue compression device to apply pressure to a transverse slice of tissue within the vertebral body so as to form a cavity anterior to the guide element.

According to a further feature of the present invention, an expandably fillable element is introduced into the cavity and introducing a filling material the expandably fillable element so as to increase an axial dimension of the vertebral body.

According to a further feature of the present invention, the expandably fillable element includes perforations such that the introducing a filling material releases a small proportion of the filling material to enhance fixation of the expandably fillable element.

According to a further feature of the present invention, the expandably fillable element is formed with a pair of flexible elongated fixation appendages, the expandably fillable element being deployed with the fixation appendages extending through the bores in the first and second pedicles, respectively, the method further comprising, after introduction of the filling material, attaching the fixation appendages to contralateral regions of the vertebra so as to fix the expandably fillable element in a required position.

There is also provided, according to the teachings of the present invention, a method for repairing an intervertebral disc having a nucleus, the method comprising the steps of: (a) positioning a net element within the nucleus of the disc, the net element having openings sufficiently large to permit penetration of tissue cells; (b) introducing into the net element a plurality of beads of material chosen to have surface properties which encourage generation of scar tissue, the beads having dimensions greater than the openings in the net element so as to be retained by the net element; (c) sealing the net element so as to prevent release of the beads; and (d) leaving the net element and the beads in position to allow generation of scar tissue on surfaces of the beads.

According to a further feature of the present invention, the beads are formed primarily from material exhibiting surface pores of width 50-100 microns, and more preferably of width 70-80 microns.

According to a further feature of the present invention, the beads are formed primarily from polypropylene.

According to a further feature of the present invention, the beads are substantially spherical.

According to a further feature of the present invention, the beads have a diameter of 1-5 mm.

According to a further feature of the present invention, the net element is anchored bilaterally to bone elements of a vertebra.

There is also provided, according to the teachings of the present invention, a method for restoration of a damaged vertebral body, the method comprising the steps of: (a) employing a directional tissue compression device to apply pressure to a transverse slice of tissue within the vertebral body so as to form a cavity; (b) introducing into the cavity an expandably fillable element and partially inflating the expandably fillable element with a filling material so as to deploy the expandably fillable element within the cavity; and (c) further inflating the expandably fillable element so as to increase a height dimension of the vertebral body.

According to a further feature of the present invention, the expandably fillable element has a plurality of perforations configured such that the inflation causes release of a small proportion of the filling material from the expandably fillable element so as to enhance fixation of the expandably fillable element.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 is a plan view of a vertebra illustrating schematically a surgical apparatus and method, constructed and operative according to the teachings of the present invention;

FIG. 2 is a schematic isometric view of the apparatus of FIG. 1;

FIG. 3A is an enlarged side view of a first preferred configuration for the distal end of rigid tubes for use in the apparatus of FIG. 1;

FIG. 3B is an enlarged side view of the distal end of the tube of FIG. 3A showing a trocar inserted within the tube for penetration of tissue;

FIG. 3C is a side view of an alternative configuration for a distal end of rigid tubes for use in the apparatus of FIG. 1;

FIG. 3D is an enlarged side view showing a directional drilling device extending from the distal tube end of FIG. 3A;

FIG. 4 is a schematic side view illustrating the use of the apparatus of FIG. 1 employed to perform a procedure on an intervertebral disc;

FIG. 5 is a schematic plan view of a preferred net element for use in the procedure of FIG. 3;

FIG. 6 is a schematic cross-sectional view showing a preferred mode of releasable connection of beads with a flexible guide element for use in the procedure of FIG. 3;

FIG. 7 is a schematic plan view illustrating the release of a chain of beads into the net element of FIG. 4 during performance of the procedure of FIG. 3;

FIGS. 8A and 8B are schematic plan views illustrating a directional tissue compression device for use in a procedure on a vertebral body according to the teachings of the present invention, the device being shown prior to and during use, respectively; and

FIG. 9 is a schematic plan view of a directionally inflating perforated expandably fillable element, constructed and operative according to the teachings of the present invention, for use in a vertebral body subsequent to said direction tissue compression device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an apparatus and method for minimally invasive spinal surgery. The invention also provides surgical techniques, advantageously implemented using the apparatus and method of the invention, for intervertebral disc repair and for vertebral body repair.

The principles and operation of a surgical apparatus and method, and surgical techniques, according to the present invention will be better understood with reference to the drawings and the accompanying description.

Surgical Apparatus and Method

Referring now to the drawings, FIG. 1 illustrates a preferred apparatus and corresponding method for performing various minimally invasive spinal surgery (MISS) procedures according to the teachings of the present invention. In general terms, the preferred surgical method of the present invention is based on inserting an elongated flexible guide element 10 such that the guide element passes in through a first lateral posterior incision, passes through the spinal column anterior to the spinal cord, and passes out through a second lateral posterior incision contralateral to the first incision. The guide element 10 is then employed to guide at least one element to a desired position within the spinal column as part of the surgical procedure.

It will be immediately apparent that the present invention offers profound advantages for performance of MISS procedures. Specifically, the guide element thus placed functions in a manner analogous to the ubiquitous guide wire of vascular surgery, defining a precise path along which other elements or devices can be advanced in a precise and repeatable manner. The device effectively provides a platform for manipulation of tissues and introduction of implants anterior to the spinal cord. The elements or devices may travel along using the guide element as a stationary rail, or the guide element itself may be advanced through the spinal column with pull-through functionality. In either case, the guide element provides a well defined reference location within the spinal column for performance of a MISS procedure. In the case of implanted devices, the guide element also facilitates bilateral fixation at the end of the procedure by attachment of portions of the guide element to bone surfaces on both sides of the vertebra. These and other advantages of the present invention will be better understood from the following detailed description.

Turning now to structural details of a preferred implementation of the present invention, the path of guide element 10 through the spinal column is preferably defined by a pair of hollow rigid tubes 12, 14 inserted through contra-lateral incisions in the back of a subject. For simplicity of representation, the soft tissue through which the incisions are made has been omitted from the drawings. Suitable incisions for such a lateral posterior approach are well known, and can typically be implemented as a small stab wound. A rigid coupling 16 is configured for rigidly coupling tubes 12, 14 such that the tubes converge towards their distal (inserted) ends but maintain a predefined gap between their ends. This gap is preferably in the range of 15-20 millimeters wide. Guide element 10 is then deployed passing in through a first of the hollow tubes 12, traversing the gap between the distal ends, and passing out through a second of the hollow tubes 14. The portion of the guide element traversing the gap defines a working region within the spinal column, as will become clearer from the subsequent examples.

FIG. 2 illustrates in more detail a preferred implementation of the apparatus. Specifically, first and second tubes 12, 14 are preferably implemented as substantially straight hollow tubes with inward-facing distal openings such that the distal openings face each other across the gap. This facilitates insertion of guide element 10 passing across the gap and helps to clearly delimit the sides of the gap. In a first preferred implementation shown here, and enlarged in FIG. 3A, the distal ends of tubes 12, 14 are implemented as inward facing beveled ends. In an alternative preferred implementation, the distal ends of first and second tubes 12, 14 are curved towards the gap as illustrated in FIG. 3C.

In order to ensure that the beveled or curved distal ends of tubes 12, 14 are correctly oriented, at least a proximal clamping portion of each tube is preferably formed so as to be asymmetrical under rotation and to cooperate with clamping elements associated with rigid coupling 16 so as to define the required orientation. Thus, in the example shown here, each tube 12, 14 has an enlarged clamping portion 12 a, 14 a with a flat surface 18 defining a clamping orientation relative to rigid coupling 16. Clamping portions 12 a and 14 a are preferably also asymmetric under reflection so as to be non-interchangeable with each other. Thus, in the example shown here, each clamping portion has a generally triangular asymmetric cross-section where only one side is flat to provide clamping surface 18 and the remainder of the surfaces are curved.

In the particularly simple implementation shown here, rigid coupling 16 is implemented with eccentric lever clamps 20 deployed in slots 22. This allows quick clamping in a range of relative spacings between the rigid tubes, but in a predefined angular relation defined by clamping surfaces of clamps 20. The angular relation is typically inclined inwards towards a central plane through the device at between 15°-25°, corresponding to an angle of conversion of the two tubes in the range of 30°-50°. Clearly, many other clamping configurations may equally be used, optionally giving additional degrees of freedom of adjustment such as an angular adjustment of the rigid tubes.

Although shown here as a free-standing structure, rigid coupling 16 may be mechanically linked through an adjustable clamping structure (not shown) to a fixed reference surface such as an operating table to provide additional stabilization and rigidity during performance of a procedure. Alternatively, the rigid coupling may be temporarily anchored to the subject's body via axial skeletal features. Suitable adjustable clamping structures for both of these types of clamping are known in the art and will not be described herein.

A wide range of materials may be used to produce rigid tubes 12, 14 and rigid coupling 16. Particularly preferred examples include, but are not limited to, surgical steel and other biocompatible metals, metal alloys and rigid polymers. The diameter of the tubes is typically in the range of 2-6 mm, and most preferably in the range of 3-5 mm.

According to a further optional feature particularly relevant to the beveled-ended implementation, a removable trocar 24 is removably received within each tube 12, 14 (FIG. 3B) to facilitate insertion of the first and second tubes through soft tissues of the subject's back to reach the desired position. The trocar is then withdrawn to free the lumen of the tube for insertion of the guide element.

It should be noted that the apparatus and method of the present invention are useful for performance of a wide range of MISS procedures, including many known procedures conventionally performed by other surgical techniques. These include procedures performed both on intervertebral discs and on the vertebral body. In the case of an intra-discal procedure, rigid tubes 12, 14 are preferably inserted immediately above the transverse processes of the vertebra below the disc in question as shown in FIG. 4. In the case of an intra-vertebral procedure, preferred positioning for insertion of rigid tubes 12, 14 is via small holes drilled through the pedicle on each side of the vertebra.

Depending upon the nature and current status of the tissue (disc nucleus or vertebral body cancellous bone) in the gap between the distal ends of the rigid tubes, it may be possible to insert guide element 10 across the gap simply be advancing it along one of the tubes, optionally with either a steering mechanism or a with a tip with a pre-formed curvature to facilitate the lateral motion required to cross the gap to reach the opening of the other tube. In other cases, however, a drilling device may be required. For this purpose, the apparatus preferably also includes a retractable drilling device 26 (FIG. 3D) removably associated with one of tubes 12, 14 so as to drill a connecting channel through the gap for insertion of the guide element. Most preferably, retractable drilling device 26 is implemented as a directional drilling device configured for drilling in a direction non-parallel with a central bore of the tube. Although thermal or laser ablation may be used for this purpose, mechanical drills are believed to be preferable to avoid risk of thermal damage to surrounding tissue (disc, bone and nerves). Examples of suitable mechanical directional drilling devices, both steerable and with a fixed lateral curvature, are known in the field and will not be described herein in detail. By way of example, two suitable designs are described in U.S. Pat. No. 6,558,386 which is hereby incorporated by reference, particularly with reference to FIGS. 9-10 thereof.

Turning now to guide element 10 itself, it should be noted that the guide element may be implemented in many different configurations varying in shape, gauge, materials and deployment according to the requirements of each given procedure to be performed. Furthermore, various different guide element configurations may be used during the course of a single procedure, either by withdrawing a first guide element and deploying an alternative guide element or by connecting different guide element configurations sequentially such that each section pulled out draws the subsequent section of the guide element into position traversing the gap within the spinal column as required. In many cases, the guide element is preferably chosen to be asymmetric under rotations of less than 180° about its length, thereby providing a defined orientation for devices introduced within the spinal column. A simple example of a preferred asymmetric form is a flat strip. Other examples will be discussed below in the context of certain specific applications. Preferred materials for the guide element are typically flexible biocompatible polymer materials such as PEEK or resilient metals or metal alloys such as spring steel or superelastic nitinol alloys.

Intervertebral Disc Repair

Turning now to FIGS. 5-7, a preferred technique for repair of a damaged intervertebral disc will now be described. It should be appreciated that, while the technique is described in a particularly preferred context implemented using the surgical method of the present invention, various aspects of the technique are believed to be patentable in their own right even if implemented using otherwise conventional surgical methods.

In general terms, the disc repair technique of the present invention is performed by introducing into the nucleus of a damaged disc a plurality of beads of material chosen to have surface properties which encourage generation of scar tissue. By using beads, the filling conforms readily to the geometry of the load-transfer surfaces of adjacent vertebrae and immediate provides load-bearing support in a manner similar to that described in U.S. Pat. No. 5,702,454. At the same time, in contrast to the teachings of that patent, the use of surfaces for encouraging generation of scar tissue initiates a physiological process in which scar tissue fills the gaps between the beads, becoming a significant if not primary contributor to the physical properties of the disc nucleus. Scar tissue, being highly fibrous, moderately flexible and having few nerves has been found by the present inventor to be an ideal substitute for the natural tissue of the inner disc.

In order to encourage scar tissue formation, the beads are preferably formed primarily, or entirely, from material exhibiting surface pores of width 50-100 microns, and most preferably in the 70-80 micron range. A preferred but non-limiting example of a biocompatible material exhibiting pores of this size is polypropylene. The beads are preferably rounded to ensure that they conform readily to the shape of the space to be filled. Most preferably, substantially spherical beads are used. A preferred diameter (or maximum dimension for non-spherical beads) is typically in the range of 1-10 mm, and most preferably around 1-5 mm.

In order to ensure correct placement of the beads within the disc, this aspect of the present invention preferably employs a net element configured to contain the plurality of beads within a defined containment region. The net element must clearly have openings sufficiently fine to prevent passage of the filling beads. At the same time, in order to facilitate the aforementioned generation of scar tissue around the beads, the openings of the net element are sufficiently large to permit penetration of tissue cells and small blood vessels. A preferred range of sizes for the net element openings is up to about 0.5 mm.

A preferred implementation of net element for use in the surgical method and apparatus described above is shown in FIG. 5 designated 30. In this case, net element 30 is attached to, or integrally formed with, an opening in the side of a piece of flexible tubing such that the portions either side of the net element provide first and second tubular flexible elongated fixation appendages 32 and 34. The functions of these appendages will be described below.

The guide element surgical method and apparatus described above offers a particularly convenient, controllable and effective manner of delivering a desired quantity of beads into the intervertebral disc. Specifically, as illustrated schematically in FIG. 6, a series of beads 36 are preferably configured to be detachably associated with an appropriately formed guide element 10 and to be released from the guide element for delivery to a desired position within the intervertebral disc. In the implementation illustrated in FIG. 6, each bead 36 is formed with a shaped recess and elongated guide element 10 is formed with a complementary sequence of projections or projecting ridge 38 forming a releasable “snap” connection. Clearly, alternative releasable connection configurations may also be used. Other examples include, but are not limited to, reverse configurations with projections from beads 36 engaging recessed in guide element 10, and integrally molded implementations where beads 36 and guide element 10 are integrally molded with small frangible attachment points which can be broken to release the beads. To ensure release of the beads from the guide element at the correct location, net element 30 is preferably provided with a release configuration deployed to effect release of the beads from guide element 10. In the example shown here, the release configuration is implemented as a forked ramp or wedge 40 located within the net element near the point where guide element 10 passes out through appendage 34.

Most preferably, in order to further reduce the risk of beads escaping from the internal disc volume, beads 36 are interconnected into strings or chains of beads by small interconnecting links. Typically, the links are integrally molded with the beads. Alternatively, the beads may be separately formed and then strung on a separate connecting strand.

In use, after positioning of rigid tubes 12, 14 and guide element 10 as described above, net element 30 is advanced in a folded state around guide element 10 until it reaches a position with the net deployed in the gap between the rigid tubes and appendages 32 and 34 deployed within tubes 12 and 14, respectively, as shown in FIG. 7. This positioning may be reliably determined by appropriate length markings on parts of appendages 32 and/or 34 extending outwards from the rigid tubes indicating the distance from the beginning of the net element. Additionally, or alternatively, imaging techniques such as fluoroscopy may be used to verify the positioning. For this purpose, radio-opaque reference markers are preferably incorporated into the net element at predefined positions.

Once the net element is in place, the portion of the guide element carrying beads 36 is advanced (typically pulled-through) to draw the beads into the internal volume of the net element. As they reach release configuration 40, the beads become detached from the guide element, thereby freeing a string of beads as shown in FIG. 7. Preferably, the deployment of the beads on guide element 10 is such that a predefined length of guide element corresponds to a quantity of beads sufficient to fill a predefined volume. For example, a given length of, for example, 5 cm of the guide element with beads may correspond to a volume of 1 cc. Thus, based on prior planning considerations of the total desired volume of the restored disc and the current volume, the corresponding required quantity of beads may be determined simply by marking-off a required length of the bead-carrying guide element to be used, and possibly severing the beads from the guide element beyond that length.

Once the desired expansion of the intervertebral disc has been achieved by insertion of the required quantity of beads, guide element 10 is removed and rigid tubes 12, 14 are withdrawn. Appendages 32 and 34 are then tied or otherwise sealed to prevent release of beads from net element 30. Appendages 32, 34 are then attached to ipsilateral regions of bone so as to: (a) seal the contents of the net inside the net; and (b) fix net element 30 in a required position. This bilateral fixation provides reliable positioning of the net element so as to avoid problematic migration of the disc filling from its intended place. The outer incisions may then be closed with adhesive tape to complete the surgical procedure.

Vertebral Body Height Restoration

Turning now to FIGS. 8A, 8B and 9, there is illustrated a preferred apparatus and technique for restoration of a collapsed or damaged vertebral body. Here too, although described in a particularly preferred context implemented using the surgical method of the present invention, various aspects of the apparatus and technique are believed to be patentable in their own right even if implemented using otherwise conventional surgical methods.

Generally speaking, the technique solves various problems associated with controlling expansion directions of inflatable elements by dividing the procedure into two stages. In a first stage, a directional tissue compression device is introduced into the vertebral body and operated to apply pressure to a transverse slice of tissue within the vertebral body so as to form a cavity anterior to the guide element. Then, once a slice-shaped cavity is formed, an expandably fillable element is introduced into the cavity and inflated with a filling material so as to increase an axial dimension of the vertebral body.

The technique of the present invention also addresses a further problem of cement leakage common to conventional procedures. Specifically, conventional vertebral body height restoration techniques typically employ an inflatable balloon which is inserted temporarily in order to achieve the desired height restoration. The balloon is then deflated and removed, and PMMA or other cement is injected into the cavity from which the balloon was removed. Such techniques suffer from lack of control over the dispersion of the cement which may leak from the vertebral body, or may set with various sharp or abrasive surface features which may subsequently pose a risk of damage to adjacent tissue or blood vessels. In contrast, by employing a permanent filling material (such as cement) for the filling process, the location of the cement is well defined and limited by the expandably fillable element so as to protect against uncontrolled leakage of the cement beyond the vertebral body.

According to a further preferred feature of this aspect of the present invention, the expandably fillable element includes perforations dispersed over its surface such that the introducing a filling material releases a small proportion (typically less than 20%, and most preferably no more than 10%) of the filling material to enhance fixation of the expandably fillable element to the bone of the surrounding vertebral body.

In the preferred context of the surgical method described above, rigid tubes 12 and 14 are first inserted through respective bores drilled in first and second pedicles, respectively, of the vertebra requiring reconstruction. Directional drilling is then typically used to form a channel across the gap between distal ends of the tubes, and guide element 10 is inserted through the vertebral body passing in through the first pedicle of the vertebra, across within the vertebral body and out through the second pedicle of the vertebra.

As mentioned earlier, a directional tissue compression device is then used to apply pressure to a transverse slice of tissue within the vertebral body so as to form a cavity anterior to the guide element. Most preferably, the device is guided by connection to guide element, although a free standing device may optionally be introduced even before insertion of the guide element. FIGS. 8A and 8B illustrate a particularly simple but effective preferred embodiment of the direction tissue compression device, designated 42. Device 42 includes a relatively rigid housing 44 with an arcuate form and having a lateral opening 46 formed near its tip. Housing 44 typically has a rectangular cross-sectional shape, although other shapes such as an oval shape are also possible. Some degree of flexibility may be required to allow housing 44 to be inserted along rigid tube 12. Within housing 44 is deployed a flexible strip. The mechanical properties of a flat strip are that it is relatively flexible for in-plane bending but resistant to sideways bending or torsional distortion. As a result, as the flexible strip 48 is advanced, confined within housing 44, it tends to bulge outwards directionally from opening 46 as shown in FIG. 8B, thereby applying pressure directionally to a slice of cancellous bone tissue lying anterior to the device (i.e., forward from the guide element and away from the spinal cord) and bounded by an outer arcuate profile, so as to open a corresponding slice-shaped cavity.

In this context, it should be noted that the term “slice” or “slice-shaped” is used herein in the description and claims to refer to any three-dimensional form bounded in part by two substantially parallel, substantially planar faces, and independent of the shape of the remaining boundaries. In the case of a cavity or void, the bounding surfaces are clearly the inward facing surfaces of the surrounding material. The term “height” and “axial” are used to refer to a dimension and direction, respectively, substantially parallel to the spinal cord. The term “transverse” is used to refer to a plane substantially perpendicular to the spinal cord.

Many suitable materials may be used to implement device 42, as will be apparent to one ordinarily skilled in the art on the basis of straightforward criteria of biocompatibility and the required physical properties. Preferred examples include various polymer materials and metals or metal alloys. Optionally, both housing 44 and flexible strip 48 may be formed from the same material with the differing degrees of flexibility being provided by suitable design of the dimensions and/or structure of the elements.

Once the slice cavity has been formed, an expandably fillable element is introduced into the cavity. A preferred implementation of an expandably fillable element, designated 50, is shown here schematically in FIG. 9. It should be noted that there is a particular synergy between the use of directional tissue compression device 42 and expandably fillable element 50 as described. Specifically, because of the presence of the well defined preformed slice cavity, the expandably fillable element expands during filling to initially deploy itself evenly over a large proportion of the lateral dimension of the vertebral body, thereby ensuring that the subsequent continued expansion acts substantially uniformly to increase an axial dimension of the vertebral body.

Most preferably, expandably fillable element 50 includes a pair of flexible elongated fixation appendages 52, 54 for providing precise positioning of expandably fillable element 50 prior to inflation and bilateral fixation on completion of the procedure, all in a manner analogous in that of appendages 32, 34 described above. Typically, one or both of appendages 52 and 54 serves also as a filling conduit for introducing filling material into expandably fillable element 50.

A wide range of biocompatible filling materials may be used to inflate expandably fillable element 50. The filling material may be a liquid, a gel, a paste or powdered or granulated solids. Preferred examples include, but are not limited to, PMMA and other cements or inert fillers, and/or various material or medicaments used for promoting bone growth or regeneration.

Most preferably, expandably fillable element 50 includes a plurality of perforations 56 such that a small proportion of the filling material is released from the surface of expandably fillable element 50 during the filling process to enhance fixation of the expandably fillable element in the surrounding tissue. The size of the perforations are chosen according to the physical properties of the filling material in order to ensure that only a small proportion is released. This fixation enhancement may be an immediate, or nearly immediate mechanical anchoring effect such as in the example of a bone cement filler, or may be part of a slower physiological process such as in the case of a bone regenerating material.

It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims. 

1. An apparatus for use in performing a minimally invasive spinal surgical procedure via a pair of bilateral stab wounds on either side of a subject region of the spine of a patient, the apparatus comprising: (a) a first hollow rigid tube having a proximal end and a distal end, said distal end for insertion through a first of the stab wounds; (b) a second hollow rigid tube having a proximal end and a distal end, said distal end for insertion through a second stab wound in the back of a patient; (c) a rigid coupling for rigidly coupling said first and second tubes such that said tubes converge towards said distal ends but maintain a predefined gap between said distal ends; and (d) an elongated flexible guide element for deployment so as to extend through said first hollow tube from said proximal end to said distal end, to traverse said gap and to extend through said second hollow tube from said distal end to said proximal end.
 2. The apparatus of claim 1, wherein said first and second tubes are implemented as substantially straight hollow tubes.
 3. The apparatus of claim 1, wherein said distal ends of said first and second tubes are implemented as inward-facing beveled ends.
 4. The apparatus of claim 1, wherein said distal ends of said first and second tubes are curved towards said gap.
 5. The apparatus of claim 1, further comprising a removable trocar removably receivable within each of said first and second tubes for facilitating insertion of said first and second tubes in the back of the patient.
 6. The apparatus of claim 1, wherein said guide element is asymmetric under rotations about its length.
 7. The apparatus of claim 1, further comprising a retractable drilling device removably associated with at least one of said first and second tubes and configured for drilling a connecting channel through said gap for insertion of said guide element.
 8. The apparatus of claim 7, wherein said drilling device is implemented as a directional drilling device configured for drilling in a direction non-parallel with a central bore of said tube.
 9. The apparatus of claim 1, further comprising a plurality of beads detachably associated with said guide element, and a release mechanism for releasing said plurality of beads from said guide element in said gap.
 10. The apparatus of claim 9, wherein said plurality of beads are interconnected as at least one chain of beads such that said plurality of beads remain interconnected after release from said guide element.
 11. The apparatus of claim 9, wherein said plurality of beads are formed from a material having a porous surface with pores of width 50-100 microns.
 12. The apparatus of claim 9, wherein said plurality of beads are formed from a material having a porous surface with pores of width 70-80 microns.
 13. The apparatus of claim 9, further comprising a net element deployable within said gap around said guide element so as to contain said plurality of beads within a predefined containment volume.
 14. The apparatus of claim 13, wherein said plurality of beads are each formed with at least one surface configured to promote scar tissue formation, and wherein said net element is formed to allow penetration of cells to facilitate scar tissue formation at said at least one surface.
 15. The apparatus of claim 13, further comprising a pair of flexible elongated fixation appendages associated with said net element so as to be locatable within said first and second tubes and adapted for fixation to bone surfaces after removal of said first and second tubes to fix said net element in a required position.
 16. The apparatus of claim 1, further comprising a directional tissue compression device removably deployable along at least one of said first and second tubes, said directional tissue compression device including at least one compression element configured for applying pressure to a slice of tissue located adjacent to said gap and extending away from said first and second tubes so as to form a cavity.
 17. The apparatus of claim 16, further comprising an expandably fillable element for deployment in said cavity.
 18. The apparatus of claim 17, wherein said expandably fillable element includes perforations configured for allowing release of a small proportion of a filler material to enhance fixation of said expandably fillable element.
 19. The apparatus of claim 17, wherein said expandably fillable element includes a pair of flexible elongated fixation appendages locatable within said first and second tubes, said fixation appendages being adapted for fixation to bone surfaces after removal of said first and second tubes to fix said expandably fillable element in a required position.
 20. A method for performing a minimally invasive spinal surgical procedure, the method comprising the steps of: (a) inserting an elongated flexible guide element such that said guide element passes in through a first lateral posterior incision, passes through the spinal column anterior to the spinal cord, and passes out through a second lateral posterior incision contralateral to said first incision; and (b) employing said guide element to guide at least one element to a desired position within the spinal column as part of the surgical procedure.
 21. The method of claim 20, further comprising: (a) inserting a first hollow rigid tube through said first incision; (b) inserting a second hollow rigid tube through said second incision; and (c) rigidly coupling said first and second tubes in spatial relation so as to define a gap between distal ends of said tubes, wherein said inserting of said guide element is performed via said first and second tubes.
 22. The method of claim 21, wherein said first and second tubes are implemented as substantially straight hollow tubes.
 23. The method of claim 21, wherein said first and second tubes are implemented with beveled ends, said rigidly coupling being performed so that said beveled ends face inwards towards said gap.
 24. The method of claim 21, wherein said first and second tubes are implemented with curved ends, said rigidly coupling being performed so that said curved ends curve inwards towards said gap.
 25. The method of claim 21, wherein a removable trocar is inserted into each of said first and second tubes for facilitating said inserting of said first and second tubes, said trocar being removed prior to said inserting of said guide element.
 26. The method of claim 21, further comprising employing a retractable drilling device inserted via one of said first and second tubes to drill a connecting channel through said gap for insertion of said guide element.
 27. The method of claim 26, wherein said drilling device is implemented as a directional drilling device configured for drilling in a direction non-parallel with a central bore of said tube.
 28. The method of claim 20, wherein said guide element is asymmetric under rotations about its length.
 29. The method of claim 20, wherein said guide element is inserted through an intervertebral disc.
 30. The method of claim 29, wherein said at least one element includes a plurality of beads detachably associated with said guide element, said plurality of beads being released for delivery to a desired position within said intervertebral disc.
 31. The method of claim 30, wherein said plurality of beads are interconnected as at least one chain of beads such that said plurality of beads remain interconnected after release from said guide element.
 32. The method of claim 30, wherein said plurality of beads are formed from a material having a porous surface with pores of width 50-100 microns.
 33. The method of claim 30, wherein said plurality of beads are formed from a material having a porous surface with pores of width 70-80 microns.
 34. The method of claim 30, wherein said at least one element includes a net element deployable around said guide element, said net element being deployed within said intervertebral disc so as to contain said plurality of beads within a predefined containment volume.
 35. The method of claim 34, wherein said plurality of beads are each formed with at least one surface configured to promote scar tissue formation, and wherein said net element is formed to allow penetration of cells to facilitate scar tissue formation at said at least one surface.
 36. The method of claim 34, wherein said net element is formed with a pair of flexible elongated fixation appendages, said net element being deployed with said fixation appendages extending through within said first and second contralateral incisions, respectively, the method further comprising, after release of said plurality of beads into said net element, attaching said fixation appendages to contralateral regions of bone so as to fix said net element in a required position.
 37. The method of claim 20, wherein said guide element is inserted through a vertebral body.
 38. The method of claim 37, wherein said guide element is inserted through a bore drilled in a first pedicle of the vertebra, passes through the vertebral body and passes out through a bore drilled in a second pedicle of the vertebra.
 39. The method of claim 37, further comprising introducing a directional tissue compression device into said vertebral body and operating said directional tissue compression device to apply pressure to a transverse slice of tissue within said vertebral body so as to form a cavity anterior to said guide element.
 40. The method of claim 39, further comprising introducing an expandably fillable element into said cavity and introducing a filling material said expandably fillable element so as to increase an axial dimension of said vertebral body.
 41. The method of claim 40, wherein said expandably fillable element includes perforations such that said introducing a filling material releases a small proportion of said filling material to enhance fixation of said expandably fillable element.
 42. The method of claim 40, wherein said expandably fillable element is formed with a pair of flexible elongated fixation appendages, said expandably fillable element being deployed with said fixation appendages extending through said bores in the first and second pedicles, respectively, the method further comprising, after introduction of said filling material, attaching said fixation appendages to contralateral regions of said vertebra so as to fix said expandably fillable element in a required position.
 43. A method for repairing an intervertebral disc having a nucleus, the method comprising the steps of: (a) positioning a net element within the nucleus of the disc, said net element having openings sufficiently large to permit penetration of tissue cells; (b) introducing into the net element a plurality of beads of material chosen to have surface properties which encourage generation of scar tissue, said beads having dimensions greater than said openings in said net element so as to be retained by said net element; (c) sealing said net element so as to prevent release of said beads; and (d) leaving said net element and said beads in position to allow generation of scar tissue on surfaces of said beads.
 44. The method of claim 43, wherein said beads are formed primarily from material exhibiting surface pores of width 50-100 microns.
 45. The method of claim 43, wherein said beads are formed primarily from material exhibiting surface pores of width 70-80 microns.
 46. The method of claim 43, wherein said beads are formed primarily from polypropylene.
 47. The method of claim 43, wherein said beads are substantially spherical.
 48. The method of claim 43, wherein said beads have a diameter of 1-5 mm.
 49. The method of claim 43, further comprising anchoring said net element bilaterally to bone elements of a vertebra.
 50. A method for restoration of a damaged vertebral body, the method comprising the steps of: (a) employing a directional tissue compression device to apply pressure to a transverse slice of tissue within the vertebral body so as to form a cavity; (b) introducing into said cavity an expandably fillable element and partially inflating said expandably fillable element with a filling material so as to deploy said expandably fillable element within said cavity; and (c) further inflating said expandably fillable element so as to increase a height dimension of the vertebral body.
 51. The method of claim 50, wherein said expandably fillable element has a plurality of perforations configured such that said inflation causes release of a small proportion of the filling material from said expandably fillable element so as to enhance fixation of the expandably fillable element. 